How would drive this MOSFET?

Apr 11, 2006 10 Replies

Given the IRF6156 Bi-Directional N-channel Switch found here:

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Let's say you had a +/-15V sine 1KHz source driving a 5.0R resistor thru this bi-directional switch to ground. How would you drive the gates to perform bi-directional switching? When switched "on" both channels must be on, parasitic diodes do not count. Why didn't they make it a common source so it is easly driven? Regards, Harry


I guess it's just easy to make.

Applications seem to be limited to switching the negative terminals of various sources. This would play hell with any smart battery communications.

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Even isolated parts would be more useful.

RL

Maybe they're just calling the outer terminals the sources since they are at an externally controlled voltage. The voltage of the inner terminals, in the off state, would be determined by the chance balance of leakage currents between the two devices.

-- john

The outside terminals are the sources and as Legg points out this MOSFET must be driven by a special driver and not suibule for most Bi-directional uses. The inner drains never float but are constrained by the parasitic diodes and are one diode drop less voltage than the most positive source. Harry

Yes, I was forgetting the diodes. But they're not parasitic, they're intentional ESD diodes. Anyway, it does look as if this thing isn't for general use.

-- john

Tell us where you can obtain MOSFETs without parasitic diodes, we all want to know. Harry

SOI ?:-)

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Say what, Silicon On Insulator?? Harry

Yep. I've done one GPS receiver on a SOI CMOS process.

SOI is also often used in circuits requiring RAD-HARD.

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.

What do you mean by parasitic? There have been mosfets without protection diodes. I blew out a number of them in the 1970's.

-- john

That's it then, you blew them all up and there's none left. You must have worked on RTL and DTL because there are none of those around either. Sorry for the Boki writing style, we went to different schools together. Harry

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